Xenon flash tubes and like high voltage discharge devices are used in aviation approach lighting systems, obstruction beacons and other high energy systems where it is desirable to vary the intensity of the light flash from high intensity in day time to lower intensity at night. A xenon flash tube intensity can be varied by changing the applied voltage but only over a narrow range with a maximum intensity 5 times the minimum intensity, whereas a range of 100 to 1 is needed to suit day, night and intermediate conditions.
Flash intensity control systems are known which switch capacitors of different energy storage capacities into the discharge circuit. Contact switches burn out or fuse and fail very quickly because the switching inevitably occurs at times during the discharge of one capacitor. At such times there will be very high current surging through the contacts between charged and partially or wholly discharged capacitors. High current vacuum tube relays can carry the surge currents but are very expensive and involve considerable additional circuitry.
It is the object of the present invention to provide a simple, low cost high voltage capacitor switching system, which avoids surges through the switching means and which permits control over a wide range, for example of 100 to 1 intensities.